McLaren driver Piastri finished fourth as Verstappen produced a flawless drive to win the 50-lap race on Sunday afternoon (AEDT) and keep his bid for a fifth-straight title alive.
And Piastri's weekend looked set to grow still worse, with he and McLaren teammate and championship leader Lando Norris reported to be at risk of disqualification.
In the hours after the race, governing body FIA reported excessive rear skid block wear on the pair's cars.
Should they be disqualified, Norris - who finished second - would have his championship lead reduced to 24 points, with Verstappen and Piastri tied in second with two rounds remaining.Â
Red Bull heavyweight Verstappen started second on the grid, but took the lead from polesitter Norris after a mistake from the British driver on the opening lap.
Verstappen, who started third in the standings behind Norris and Piastri, claimed his sixth win of the year with a monster 20.741-second buffer.
It was his 69th-career victory and eighth consecutive podium.
Mercedes driver George Russell was third after fierce attempts to usurp Norris, with rookie teammate Kimi Antonelli crossing the line in fourth.
A five-second penalty to Antonelli for a false start promoted Piastri to fourth.
Norris, while missing an opportunity to claim three straight wins from pole, at least extended his lead to 30 points over his Australian teammate as the cars crossed the finish line.
Verstappen, at that stage, was 42 points adrift leading into the final two rounds in Qatar and Abu Dhabi, pending the FIA's investigation into the McLaren pair's cars.
Piastri has now failed to podium in his past six races, after leading the championship by a season-high 34 points following the Dutch Grand Prix in August.
"I don't really know what to think," Piastri told Sky Sports.
"Obviously, I need more than (cutting into the lead) now.
"The championship picture is what it is. We'll see what I can do."
Verstappen was similarly wary of getting ahead of himself.
"It's still a big gap, but we always just try to maximise everything that we've got and this weekend, that was first," Verstappen said.
Norris had brilliantly defended against Verstappen off the starting line but went too wide on the way to turn one, with the gap also allowing compatriot Russell to sneak into second.
"I let Max have a win. I let him go, let him have a nice race," Norris joked.
"No, I just braked too late - it was my F-up."
Piastri was just as unlucky in a chaotic start, making contact with New Zealand's Liam Lawson before tumbling to seventh.
Racing Bull rookie Lawson had suffered heavy damage to his front right wing and finished 16th after qualifying sixth.
Piastri escaped sanction for the collision, with Lawson appearing to turn into the side of the McLaren after braking heavily to avoid Russell.
The Melburnian had been handed a controversial 10-second penalty a fortnight ago in Brazil for a three-way crash with Antonelli and Charles Leclerc, in a huge blow to his title hopes.
Sauber rookie Gabriel Bortoleto and Aston Martin driver Lance Stroll did not cross the finish line in Las Vegas after a race-ending collision on the opening lap.
Bortoleto is set to come under investigation for making contact with Stroll at the first corner.
Ferrari racer Lewis Hamilton recovered from 19th following a disastrous qualifying performance to finish 10th, but the seven-time world champion cut a dejected figure.
"It's been the worst season ever, and no matter how much I try, it just keeps getting worse," Hamilton said.
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